The present invention is related to symmetrical oscillators of the push-push configuration and, more particularly, to push-push symmetrical oscillators from which multiple outputs may be obtained or from which outputs may be obtained from portions of the oscillator other than from an inductive element.
Symmetrical push-push oscillators have become popular for use in countermeasures and surveillance systems, test signal generators, military electronic systems, and telecommunications equipment. These oscillators are typically designed for use in the 2.0-20 GHz range. FIG. 1 is a simplified circuit diagram of a common-collector bipolar transistor implementation of a, known push-push symmetrical oscillator 1. The symmetrical oscillator 1 includes an inductor Lr, a first bipolar transistor Q1, a second bipolar transistor Q2, first and second capacitors C1, C4, first and second shunt capacitors C2, C5, and first and second feedback capacitors C3, C6. The first and second capacitors C1, C4 connect each end of inductor Lr to respective bases of transistors Q1 and Q2. Each of transistors Q1, Q2 include a respective one of the shunt capacitors C2, C5 across its base-emitter terminals. Respective ones of the feedback capacitors C3, C6 are coupled between the collector-emitter terminals of transistors Q1, Q2. The collectors of transistors Q1, Q2 are connected to ground. The inductor Lr has a center tap from which an output signal at node 2 is taken. Assuming that inductor Lr may be represented by two equal inductances L on each side of the center tap, and an equivalent capacitatance C exists from each inductance L to ground, a fundamental resonant frequency Fr may be obtained that adheres to the following equation:
Fr=1/(2n(LC)).
Due to non-linearities of the electrical components of the symmetrical oscillator 1, currents flowing in the circuit include frequency components at the fundamental resonant frequency, F, twice the fundamental resonant frequency, 2F, etc. When the symmetrical oscillator 1 is properly tuned, transistors Q1 and Q2 operate 180xc2x0 out of phase with one another and, therefore, voltages at the fundamental resonant frequency F cancel at the electrical center of inductor Lr. Further, voltages at twice the fundamental resonant frequency, 2F, are additive at the electrical center of inductor Lr and, therefore, an output signal taken at the center tap 2 will be rich in energy at 2F. Additional details concerning the operation of the symmetrical oscillator 1 of FIG. 1 may be found in John R. Bender and Colmon Wong, PUSH-PUSH DESIGN EXTENDS BIPOLAR FREQUENCY RANGE, Microwaves and RF pp. 91-98 (October 1983), the entire disclosure of which is hereby incorporated by reference.
It would be desirable to obtain two output signals from a symmetrical oscillator, one at the fundamental resonant frequency, and the other at twice the fundamental resonant frequency. Preferably each output would be electrically and/or mechanically isolated from one another. It would also be desirable to obtain an output signal at twice the fundamental resonant frequency of the symmetrical oscillator, which output signal enjoys a relatively high power level and a substantially flat response over a frequency range of interest. It would also be desirable that the output signal be taken from a point in the circuit other than from a tap on the inductor or through inductive coupling.
In accordance with at least one aspect of the invention, a symmetrical oscillator includes: a first active component having a drive terminal and first and second gain terminals, one of the first and second gain terminals of the first active component being coupled to a first reference node; a second active component having a drive terminal and first and second gain terminals, one of the first and second gain terminals of the second active component being coupled to the first reference node; a reactive element coupled between the drive terminals of the first and second active components, the reactive element at least partially defining a fundamental resonant frequency; a first feedback circuit having at least one reactive component coupled between the other of the first and second gain terminals of the first active component and a common node; and a second feedback circuit having at least one reactive component coupled between the other of the first and second gain terminals of the second active component and the common node, wherein an output signal is taken from at least one of the reactive element, the common node, and the first reference node.
In accordance with at least one other aspect of the invention, a symmetrical oscillator includes: a first active component having a drive terminal and first and second gain terminals, one of the first and second gain terminals of the first active component being coupled to a first reference node; a second active component having a drive terminal and first and second gain terminals, one of the first and second gain terminals of the second active component being coupled to the first reference node; a first reactive element coupled between the other of the first and second gain terminals of the first active component and the drive terminal of the first active component; a second reactive element coupled between the other of the first and second gain terminals of the second active component and the drive terminal of the second active component, the first and second reactive elements at least partially defining a fundamental resonant frequency; a first shunt circuit having at least one reactive component coupled between the drive terminal of the first active component and a common node; and a second shunt circuit having at least one reactive component coupled between the drive terminal of the second active component and the common node; and a feedback circuit coupled between the others of the first and second gain terminals of the first and second active components, wherein an output signal is taken from at least one of the feedback circuit, the common node, and the first reference node.
In accordance with at least one other aspect of the invention, a symmetrical oscillator includes: a first active component having a drive terminal and first and second gain terminals, the drive terminal of the first active component being coupled to a first reference node; a second active component having a drive terminal and first and second gain terminals, the drive terminal of the second active component being coupled to the first reference node; a reactive element coupled between one of the first and second gain terminals of the first active component and one of the first and second gain terminals of the second active component, the reactive element at least partially defining a fundamental resonant frequency; a first shunt circuit having at least one reactive component coupled between the other of the first and second gain terminals of the first active component and a common node; and a second shunt circuit having at least one reactive component coupled between the other of the first and second gain terminals of the second active component and the common node, wherein an output signal is taken from at least one of the reactive element, the common node, and the first reference terminal.
Other objects, features, and/or advantages will become apparent to one skilled in the art in view of the disclosure herein.